NASA has confirmed that the New Horizons probe has emerged from its 321-day hibernation. The signal was received at the Deep Space Network station located near Madrid.
The NASA Deep Space Network (DSN) station, situated in Robledo de Chavela (Madrid), witnessed a space milestone. At 08:52 hours (local time) on June 23, it received the signal from the New Horizons probe, which had awakened after 321 days in hibernation. The spacecraft is approximately 9.5 billion kilometres from Earth, at the edge of the Solar System.
The signal was not a response to an order sent from Earth. Before entering sleep mode, engineers uploaded a sequence of instructions into the onboard computer that indicated when the probe should reactivate. New Horizons executed that programming on June 23 and, without the need for a new command from Earth, powered up its systems and transmitted a message. The signal took about eight hours and 52 minutes to reach the Madrid antenna.
An autonomous machine 9.5 billion kilometres away
The hibernation did not mean a total shutdown. During those 321 days, most systems remained off to save energy and reduce wear, but the flight computer continued to monitor the overall status while the spacecraft stably rotated on its axis. Once a week, it sent a simple beacon to indicate that everything was in order. This way, the mission team could know that the probe was healthy without maintaining constant communication.
The command and data management system relies on a 12 MHz Mongoose V processor, radiation-hardened and designed to withstand extreme conditions. This component distributes commands among the subsystems and executes routines that allow the probe to react without immediate intervention. In the event of failures, the spacecraft can initiate recovery or switch to backup components. At that distance, autonomy is not a luxury but a necessity for survival.
New Horizons' observations are stored in two 8 GB solid-state units, one primary and one backup. Although this memory seems insignificant compared to current devices, in deep space it requires careful management of every piece of data. The team must prioritise and wait for the spacecraft to be able to point correctly towards Earth to transmit.
Nuclear power and stellar navigation
New Horizons does not rely on solar panels but on a radioisotope thermoelectric generator that harnesses the heat from the decay of plutonium-238 to produce electricity. The power decreases slowly over the years, so every instrument powered on involves a decision. Insulating layers retain the heat generated by the electronics, and automatic heaters intervene when necessary.
To orient itself, the spacecraft observes the stars and compares them with an onboard catalogue. Then, its small thrusters adjust the position to align the main antenna with Earth. This antenna cannot move independently, so the entire vehicle must be positioned correctly before beginning the data transmission. Only then do the data embark on a journey of nearly nine hours to the Robledo de Chavela station.
The paradox of hibernation is that New Horizons continued to conduct science. Three instruments—SWAP, PEPSSI, and the Venetia Burney counter—remained active to study particles, plasma, and dust in the environment. The measurements were stored for when regular communication could resume. The mission had reduced its activity but not its capacity to observe.
For the residents of Robledo de Chavela, this NASA station is a silent pride. There, among oaks and pastures, 70-metre antennas listen to the whispers of spacecraft that have travelled beyond what any human has reached. And on June 23, one of those antennas was the first to know that New Horizons was still alive, awake, and ready to continue its journey into the unknown.
